N95 mask and micro wave

 As the world battles a global pandemic, healthcare and frontline workers have been pushed to the forefront to deal with more than just the disease– and often without proper protection. The new novel coronavirus doesn’t have a vaccine so far, and PPE and N95 masks are in short supply as nobody (not even the developed countries) were prepared to deal with a pandemic this size.

While the production of PPEs has been significantly amped up, with different companies pitching in to support the cause, the supply-demand chain is still disproportionate.

An Indian PhD student from Harvard University, who is currently at the forefront of the crisis in the USA, has found an innovative way to decontaminate an essential commodity for medical workers: The n95 masks.

Tanush Jagdish, an Indian national from Bengaluru, is PhD Candidate in the Program for Systems, Synthetic and Quantitative Biology at Harvard University and Graduate Student Fellow at the Center for Computational and Integrative Biology at Massachusetts General Hospital, and at the forefront of the battle with COVID-19.

His solution to decontaminating the masks? Microwave them. And no, this isn’t a ‘jugaad’ method, there’s actual science behind it.

Jagdish tested the decontamination process by putting an N95 mask atop a glass container filled with water and a mesh net separating the mask and microwaving it.

While he didn’t test it on the actual new strain of COVID-19, he did test it on a very similar virus – MS2.

“MS2 is a virus which infects the bacterium E. coli, not humans. We can make billions of new MS2 everyday by infecting E. coli with old MS2 and harvesting new MS2 once the E. coli are infected. We can also use a method called ‘plaque assays’ to measure how many viruses remain on masks. For this, we take all the viruses on a mask and add them on to E. coli growing on a petri dish. The viruses will make little holes or ‘plaques’ in the E. coli. By counting the number of plaques on the petri dish, we can extrapolate and back-calculate how many viruses were on the mask in the first place,” he explained.

MS2 however, isn’t the same as COVID-19, but there are obviously many factors linked to using the new novel coronavirus strain – the difficulty of using a new strain, the risk of infection, and a break-out and spread from the laboratory, and a potential outbreak.

But MS2 is a pretty good substitute, and also an indicator on why the results would work on COVID-19.

“The MS2 virus gives us speed, efficiency, and safety in testing, and is also a good alternative to SARS-CoV-2 because MS2 has a genome structured similar to SARS-CoV-2. They both have a single positive strand RNA as their genomes. But the outer structure of MS2 is still different from SARS-CoV-2. MS2 has an icosahedral protein capsid while SARS-CoV-2 has a lipid membrane as its covering. This, however, works in our favor because a protein capsid is more resilient and harder to decontaminate than a lipid membrane. So, a method that works on MS2 will likely be stronger than actually needed for SARS-CoV-2 with its weaker lipid membrane.”

Jagdish explained how he came up with the idea of microwaving the mask from the most basic idea of decontamination: heat.

Heat is generally one of the easiest methods used in decontamination across all major laboratories and hospitals, the primary sterilization method for reagents and instruments is high heat under high pressure.

“Steam is incorporated within these methods because it can permeate through layers and increase the overall surface area and volume of decontamination. Moist heat is known to be much better at killing microbes because it denatures the overall structures of important enzymes, which end up coagulating and crashing out of solution,” he said.

Another important point to consider in the process was a function – the N95 didn’t just need to be decontaminated, it needed to be re-usable.

“Using chemical disinfection methods is not possible here because N95 masks have layers with certain electrostatic interactions that can be easily disturbed by ethanol or disinfectant sprays. Using just dry heat is possible because SARS-CoV-2 is known to be unable to survive past 70 degree Celsius,” he said.

But using dry heat also comes with a problem – it damages the mask, rendering it ineffective, which is where steam becomes a viable solution. “Steam permeates through the layers and kills the remaining viruses, but the 3-minute timescale inside a microwave preserves the N95 mask fit and functionality,” Jagdish said.

The Harvard student also ensured that the masks were fit to wear after the procedure.

“There are seven tests recommended by the United States Occupational Safety and Health Administration (OSHA) and our microwave-decontaminated masks passed them all. Specifically, we used a PortaCount Pro Fit Tester for quantitative fit testing using sodium chloride as the test aerosol. These tests have been conducted before in other studies as well, and filtration has not been reported to be affected,” he said.

However, there is more than just fabric and mesh layers to a N95 mask – there is metal. Metal straps present in an N95 mask on the bridge of the nose help hold it together, and the same metal, which can potentially interfere with working of the microwave.

Jagdish, however, said that the process is still safe. “If the metal has pointy ends (such as forks or nails), these surfaces can act like ‘antennas’ and generate electrical sparks, but the metal strips on N95 masks tend to be aluminium and are smoothly curved. The curvature of the metal prevents arcing (electric sparks) and the presence of water and steam prevents excessive heat.”

He advised that if people are working with other kinds of masks which have jagged or pointy ends and more metal present in them other than a thin strip, they should definitely not try the method, which could lead to sparks and cause an outage or an explosion.

He also would not recommend this decontamination method, unless you absolutely have to.

“Many practices that are supposed to be last resorts are starting to become common in many states and countries. Because so many hospitals had started simply extending their use of N95 (or reusing without decontamination), the CDC now has official guidelines on how to disinfect masks. One of the guidelines recommended by CDC and approved by the FDA is the use of vaporized hydrogen peroxide (VHP). Our team did initial work that helped showcase its effectiveness. While VHP is an excellent method, it is still only limited to big hospitals with the resources to afford VHP chambers,” he said.

However, he added that with PPE disinfection protocols becoming a common thing now owing to the global shortages, it is vital to find disinfection methods are effective and equitably usable by everyone.

For Jagdish, working in the research wing of a hospital during a pandemic has been ‘different’. He said that collaboration among scientists has increased and the turn-around time for experiments has come down by orders of magnitudes, because it’s all hands on deck. “It’s been humbling to be part of a vast effort to help combat this virus,” he said.

He believed that the method could potentially be useful in India. He said that complex methods like VHP decontamination are unlikely to be useful across many parts of India if N95s or other PPEs were to become scarce.

The simple process of microwave steam, however, is much more accessible.

A pre-print of his research, which was made in collaboration with Kate E Zulauf, Alex B Green, Alex N. Nguyen Ba, Tanush Jagdish, Dvir Reif, Robert Seeley, Alana Dale, James E Kirby, is available online, for those looking into details about the decontamination process.


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